1. Field of the Invention
The present invention relates to a method of bonding members having different coefficients of thermal expansion. More particular, the invention relates to a suitable method of bonding a ceramic member and a metallic member.
2. Related Art Statement
As a method of bonding members having different coefficients of thermal expansion, there has been known a bonding method in which bonding is carried out while a separate intermediate layer is provided at an interface between the members. For instance, Japanese Utility Model Application Laid-open No. 59-160,533 discloses a method in which bonding is carried out while a cladding material made of W or Mo is interposed between a ceramic member and a metallic member as a bonding structure.
However, since a residual stress is developed at the bonding interface due to a difference in thermal expansion in the above-mentioned conventional method, sufficient bonding strength can not be obtained. Bonding of a metallic member and a ceramic member is by way of example explained with reference to FIG. 9. When a metallic member having a larger coefficient of thermal expansion and a ceramic member having a smaller coefficient of thermal expansion are bonded in a normal configuration prior to cooling and then are cooled, the metallic member undergoes a greater shrinkage, and as shown in FIG. 9, a tensile stress is imposed upon both the metallic member and the ceramic member at an end portion A of the interface. If such a state further proceeds, peeling or cracking sometimes takes place from the interface end portion A.